BackgroundIn ammation is the primary pathological phenomenon associated with disc degeneration; accordingly, the in ammatory cytokine tumor necrosis factor (TNF-α) plays a crucial role in disc degeneration. M1 macrophages produce proin ammatory cytokines that facilitate the progression of intervertebral disc degeneration (IDD).However, the anti-in ammatory and regenerative effects of M2 macrophages on nucleus pulposus cells (NPCs) in IDD progression remain unknown. Here, we aimed to determine the role of M2 macrophages in IDD progression. MethodsM2 conditioned medium (M2CM) was harvested and puri ed from THP-1 cells; it was then used for culturing human NPCs and a mouse intervertebral disc (IVD) organ culture model. NPCs and IVD organ models were divided into the following three groups: group 1 was treated with 10% fetal bovine serum to actas the control, group 2 was treated with 10 ng/ml TNF-α, and group 3 was treated with 10 ng/ml TNFα and M2CMto act as the co-culture group. After 3 to 14 days, cell proliferation (CCK-8 assay and western blotting for proliferation markers), extracellular matrix synthesis (quantitative polymerase chain reaction, western blotting, and immuno uorescence), apoptosis (TUNEL staining and western blotting), and NPC senescence (senescence-associated beta-galactosidase staining and western blotting) were assessed. ResultsCD206 and interleukin (IL)-10 levels were increased after 48 h of induction for M2 macrophages (both p<0.01). Cell proliferation was decreased in TNF-α-treated NPCs and was inhibited by M2CM co-culture.Moreover, TNF-α treatment enhanced the apoptosis, senescence, and expression of in ammatory factorrelated genes, including IL-6, MMP-13, ADAMTS-4, and ADAMTS-5, whereas M2CM co-culture signi cantly reversed these effects. M2CM promoted aggrecan and collagen II synthesis but reduced collagen Iα1 levels in TNF-α treatment groups. Using our established three-dimensional murine IVD organ culture model, M2CM suppressed the inhibitory effect of TNF-α of the TNF-α-rich environment. ConclusionsCollectively, these results indicate that M2CM promotes cell proliferation and extracellular matrix synthesis and inhibits in ammation, apoptosis, and NPC senescence. This study therefore highlights the therapeutic potential of M2CM for IDD.

Macrophage infiltration and polarization during lumbar intervertebral disc herniation (LDH) have attracted increased attention but their role remains unclear. To explore macrophage polarization in herniated nucleus pulposus (NP) tissue of patients with LDH and investigate the association between cell frequency and different clinical characteristics or symptoms, we conducted a retrospective study by analyzing NP tissue samples from 79 patients. Clinical features and symptoms, using the visual analog scale (VAS) and Oswestry disability index (ODI), were collected. The macrophage markers CD68, CCR7, CD163, and CD206; pro‐inflammatory cytokine TNF‐α; and anti‐inflammatory factor IL‐4 were analyzed by immunohistochemistry. The frequency of polarized macrophages and positivity rate of pro‐ and anti‐inflammatory cytokines showed significant differences in some of clinical characteristics. Specifically, higher CCR7+ and TNF‐α + proportions were identified in the high‐intensity zone (HIZ) and the type of extrusion and sequestration NP tissue than in non‐HIZ and protrude NP tissue. Higher CD206+ and IL‐4+ proportion were detected in Modic changes. However, no differences in gender, age, smoking status, Pfirrmann grade, analgesic use, leg pain duration, and segments were found between groups. CD68+, CCR7+, and CD206+ cell proportions, and TNF‐α and IL‐4 showed positive associations with VAS scores preoperation. Associations between ODI and the macrophages markers were weak/insignificant. Our results indicated that macrophage polarization or macrophage‐like cells contribute to LDH pathological features. Macrophage populations displaying significant associations with VAS score reflected continuous M1/M2 transition contributing to pain during LDH. These findings may contribute to enhanced/personalized pharmacological interventions for patients with LDH considering pain heterogeneity.

Background Low back pain or sciatic pain because of lumbar intervertebral disc herniation (LDH) is caused by mechanical compression and/or an inflammatory component on the nerve root. However, it is difficult to define to what extent each component contributes to the pain. This study attempted to explore the effects of macrophage polarization on clinical symptoms in patients experiencing LDH after surgery, and investigated the association between macrophage cell percentages and clinical efficacy. Methods This study retrospectively harvested nucleus pulposus (NP) tissue samples from 117 patients. Clinical symptoms and efficacy using the visual analog scale (VAS) and Oswestry Disability Index (ODI) were evaluated at different time points preoperatively and postoperatively. CD68, CCR7, CD163, and CD206 were selected as macrophage phenotypic markers. Results Seventy‐six samples showed positive expression of macrophage markers in NP samples of patients with LDH, whereas 41 patients displayed negative results. No significant differences were detected between the two groups, involvement of several demographic data, and preoperative clinical findings. With respect to the macrophage‐positive group, no significant correlation was detected between the positive rate of the four markers and the VAS score or ODI after surgery. However, patients with NP samples positive for CD68 and CCR7 expression showed significantly lower VAS scores 1 week after surgery compared with those in the negative group. Moreover, the improvement in VAS score showed a strong positive correlation with CD68‐ and CCR7‐positive cell percentages. Conclusions Our results indicated that pro‐inflammatory M1 macrophages may be associated with the reduction of chronic pain after surgery. Therefore, these findings contribute to better personalized pharmacological interventions for patients with LDH, considering the heterogeneity of pain.